LRO Operations at the MLRS

1
LRO Operations at the MLRS

• Jerry R. Wiant
• Randall L. Ricklefs
• Peter J. Shelus
• Center for Space Research and
• McDonald Observatory
• The University of Texas at Austin

2
Introduction

• The Lunar Reconnaissance Orbiter (LRO) will
  perform laser altimetry of the moon and improve
  lunar gravity field modelling.
• To augment orbital accuracy for lunar gravity
  field mapping, one-way laser ranging is needed to
  provide several-cm position accuracy.
• MLRS is one of the primary laser stations that
  will track LRO.
• MLRS pointing, tracking, beam-divergence,
  software, and procedural issues must be resolved
  prior to the early-2009 launch.

3
Hardware Issues - 1

• Pointing and tracking
• LRO will not be visible in the MLRS telescope, so
  accurate blind pointing is required.
• Absolute pointing of the MLRS telescope is around
  10 arcsec. Pointing to LRO will be improved (to
  1-2 arcsec) by offsetting from lunar features,
  possibly using the XY stage.
• MLRS can hands-off track high satellites to a few
  arcseconds over 15 minutes. Observer will
  re-center with lunar features as needed for 60
  minute LRO passes.

4
Hardware Issues - 2

• Energy delivered to spacecraft
• Critical to safety of LOLA detectors
• Depends on laser energy, seeing, and beam
  divergence
• Beam divergence (controlled by defocus of MLRS
  telescope) has been poorly known
• Ranging high satellites (Glonass) using high
  laser energy and high detector amplification
  while manually scan through the laser beam along
  track and cross track gives us beam divergence.

5
Hardware Issues - 3

• Energy delivered to spacecraft (cont.)?
• Tests with collimated beam showed beam-width at
  the space craft matches seeing estimate.
• Tests with LAGEOS-level defocussed beam, showed a
  beam divergence of xx arcsec.
• Tests with LEO defocussing gave yy arcsec.
• Using LEO beam divergence and LEO power will
  deliver proper power at LRO. TBD for sure

6
Hardware Issues - 4

• Optimal fire rate for LRO is 28Hz, synchronized
  with the satellite. However, MLRS will fire at 10
  Hz as usual.
• The ranging detector will be used during LRO
  ranging to gather internal calibration data and
  the firing time.
• Laser wavelength tests have confirmed
  compatibility with LRO/LOLA detector.

7
Acquisition System Software Tasks

• Allow any target to be treated like an LLR or SLR
  target through a set-up file (to allow lunar
  feature offset pointing for LRO). Done.
• Pass CPF file target type (slr, llr, xponder)
  through raw data to trigger transponder
  processing in reduction software. Done.
• Read and act on LRO go/no-go flag. Done.

8
Reduction System Software Tasks

• Download and process LRO predictions and
  schedule. Done.
• Recognize LRO by target type in raw data. Done.
• Apply one-way calibrations. Investigating.
• Convert LRO data to CRD. Done as part of CRD
  conversion.
• Send LRO data to HTSI. No change.

9
Procedure Changes

• Check integrated target schedule for LRO
  availability (1 hour out of every 2 while moon is
  above horizon).
• Manually set laser power and focus to LRO values.
• Use LRO website for operator pointing feedback,
  as there are no returns from LRO.

10
Conclusion

• Our build-up to LRO tracking has required
  addressing lingering questions about MLRS's
  pointing, tracking, and beam divergence
• Once these questions were/are answered, LRO
  tracking mainly impacts software and procedures